1. Field of the Invention
The present invention relates to a hand lever device for operating a driven member, such as a throttle valve, of an internal combustion engine via a cable. In particular, the hand lever is preferably mounted on a working machine, such as a hedge trimmer or brush cutter, in the vicinity of a hand grip so that it is easy and convenient to operate such a throttle valve or the like via a throttle cable or the like.
2. Description of the Prior Art
For example, a working machine, such as a hedge trimmer and brush cutter, comprises an operative portion including a cutting blade or the like driven by an internal combustion engine. A hand lever device is provided in the working machine for controlling the degree of opening of a throttle valve of the internal combustion engine. Such a hand lever is mounted in the vicinity of a grip of a U-shaped handle, a bar handle or the like of the working machine so as to provide manual control of the output force of the internal combustion engine.
The hand lever device is generally provided with a throttle trigger (throttle lever) operated by operator's fingers with the throttle lever being pivotally operated to thereby control the degree of opening of the throttle valve via a throttle cable. In general, the throttle valve is always biased toward the direction of minimum valve opening that allows the engine to idle. Accordingly, the throttle valve is normally kept at the idle opening position and, when the throttle cable is drawn in a predetermined amount to eliminate play, it begins to open from the opening position for idling (slow running) of the engine toward an opening position for operation (higher running speed) of the engine.
Such known hand lever devices for controlling throttle valve settings include an automatic return to an idle setting type and an immobilizable type. In the former type, when such a throttle lever is released from a pivotally operated position, the lever is automatically returned to its original idle position setting, thereby moving the throttle valve to its idle setting. In the latter type, when fingers are released from a throttle lever, the throttle lever is held immobilized at a desired pivotally operated position (see Japanese Examined Utility Model Publication No. 19944/1982, etc.).
In the auto-return type, when fingers are released from the throttle lever, the engine is automatically returned to the idling condition. Consequently, when the auto-return type is used in a working machine, where the output force of the engine is transmitted to an operative portion including a cutting blade via a centrifugal clutch, the centrifugal clutch is disconnected to cut off the transmission of the driving force to the operative portion. Accordingly, the operation of the machinery can immediately be stopped by returning the throttle valve to the opening degree for idle running if an accident occurs, thereby advantageously attaining improved safety. On the other hand, the throttle valve must be held continuously by fingers at a desired pivotal operation position to achieve the desired operation of the machinery. This causes problems in that this type is awkward with respect to intermediate opening degrees, the fingers are susceptible to fatigue, and the speed of the engine is likely to be unstable.
In general, for operational convenience, it is desired that a lever which is manually operated to pivot, for example, a throttle lever which is alternatively shifted between a released position and a set position (gripped position), without being suspended at any intermediate position. Accordingly, it is preferred in terms of operability that the lever be set in the same pivotal operation position (set position) regardless of whether an intermediately open condition (partially open condition) or the fully open condition (W.O.T.) of a throttle valve is intended.
On the other hand, the immobilizable type is capable of solving the above problems associated with the auto-return type. The immobilizable type advantageously holds the throttle lever at a desired pivotal operation position without the throttle lever being held by the operator's fingers. This enables easy cutting operation because the operator's fingers are liberated from holding it. However, since additional operation is required to release the throttle lever from the immobilized position, it is impossible to immediately stop the machinery even if an accident occurs. Accordingly, there is a problem that, in terms of safety, the immobilizable type is inferior to the auto-return type.